Taking to Twitter, Frances posted, "You have such an incredibly beautiful soul. I love you but you already knew that. Whenever wherever u need me, I'll be there". The tweet has since been removed.

Significant members of the music world have also posted messages of condolence on the social media site since Williams' death on Monday morning (August 11).

Liam Gallagher, Rihanna, Ringo Star and Ozzy Osbourne were among those to pay their respects, while a host of Hollywood figures have also come out in praise of the 'Good Will Hunting' star.

As reported, the actor died aged 63 from at his California home.

A statement made by the assistant chief deputy coroner of Marin County revealed the cause of death to be "suicide due to asphyxia" and advised "a comprehensive investigation must be completed before a final determination is made".

Confirming the news in a statement, Williams' publicist said: "Robin Williams passed away this morning. He has been battling severe depression of late. This is a tragic and sudden loss. The family respectfully asks for their privacy as they grieve during this very difficult time."